Selective W deposition on TiSi.sub.2 has been found to cause several unique problems as noted by Broadbent et al, J. Electrochem. Soc. 133:1715-1721 (1986). These problems include oxygen (O) contamination at the W-TiSi.sub.2 interface, residual TiF.sub.3 at the W-TiSi.sub.2 interface, and the depletion of Si from the TiSi.sub.2 surface during the selective W deposition. The most prevalent of these problems is the large level of interfacial O contamination and as a result, O contamination has been widely discussed in the literature.
Several authors have shown that the native oxide (TiO.sub.2 or SiO.sub.2) present on the substrate (TiSi.sub.2 or Si) prior to the selective W deposition is a source of the O contamination observed at the W-TiSi.sub.2 or W-Si interface. Wong, et al, J. Electrochem. Soc. 134: 2339-2345 (1987), showed that the presence of a native oxide on the Si substrate prior to the selective W deposition results in a significantly larger interfacial O concentration than does the case without a native oxide. Busta and Tang, J. Electrochem. Soc. 133:1195-1200 (1986), showed that the native oxide thickness on Si prior to the selective W deposition correlated with the interfacial O concentration, but could not account for the large O signal observed. They found that a native oxide thickness greater than approximately 4 nm prevented W deposition entirely. Chen et al, J. Vac. Sci. Technol.; B5, 1730-1735 (1987), observed a large O and F concentration and poor W adhesion if the surface oxide (TiO.sub.2) was not removed by a HF based clean prior to the selective W deposition.
Titanium disilicide, a useful contact barrier, is commonly employed as the cladding layer in the source, drain and gate electrode regions Because of the wide need for metalization of semiconductor devices and for the selective deposition of tungsten and other elements on encroachment barriers such as titanium disilicide, it is important to develop Very Large Scale Integration (VLSI) processes which result in interfaces that are free of contamination.